|Publication number||US7863936 B1|
|Application number||US 12/785,505|
|Publication date||Jan 4, 2011|
|Filing date||May 24, 2010|
|Priority date||Dec 1, 2009|
|Publication number||12785505, 785505, US 7863936 B1, US 7863936B1, US-B1-7863936, US7863936 B1, US7863936B1|
|Inventors||Chih-Min Liu, Ping-Hung Yin, Kuo-Chan Huang|
|Original Assignee||Himax Imaging, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (18), Referenced by (10), Classifications (10), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This continuation-in-part application claims the benefit of co-pending U.S. application Ser. No. 12/628,226, filed on Dec. 1, 2009, and incorporated herein by reference.
1. Field of the Invention
The present invention relates to a driver, and more particularly, to a low-power high-speed driving circuit with auto-calibration and pre-emphasis functionalities.
2. Description of the Prior Art
As the resolution of image sensors or displays increases, the data rate becomes very high. As a result, a requirement for a high-speed driver with superior performance grows. For all kinds of high-speed drivers, a low voltage differential signal (LVDS) technique is frequently utilized due to a lower electromagnetic interference (EMI), lower power consumption and a better signal integrity than that of a conventional CMOS full swing driver. Please refer to
Signals transmitted through a long transmission distance suffer from the loss of the high-frequency part of the transmitted signals; therefore, a conventional driving circuit usually employs a pre-emphasis functionality to emphasize the transmitted signal at its rising and falling parts, i.e., enhancing high-frequency components of the transmitted signal. The conventional pre-emphasis functionality, however, usually requires additional circuitry and will inevitably entail higher fabrication costs.
In addition, as the data rate rises up to giga bits per second (Gbps) and the cable length becomes longer, the impedance matching issue becomes crucial to prevent signal reflection at both the transmitter and receiver side. For the LVDS driver 100 shown in
Please refer to
For some applications, the applied driver has to further fulfill other specification requirements: for example, the Mobile Industry Processor Interface (MIPI) standard demands a very low supply voltage of 0.4V, and a common mode voltage of 0.2V while maintaining an output swing of ±0.1 V. In this case, a tail current source connecting reference ground cannot be applied. Please refer to
In light of this, an exemplary embodiment of the present invention provides a novel driving circuit (e.g., a novel LDVS driver) capable of achieving the same performance with less power consumption and supporting the pre-emphasis functionality without the addition of complex circuitry.
An exemplary driving circuit of the present invention comprises at least a driving unit having a first bias component, a second bias component, a first pre-emphasis units, a second pre-emphasis unit, a transmitter unit, a first processing unit and a second processing unit. The first bias component has a first node coupled to a first reference voltage, and a second node for outputting a first bias current. The second bias component has a first node for draining a second bias current, and a second node coupled to a second reference voltage different from the first reference voltage. The first pre-emphasis unit receives a first driving signal and a first pre-emphasis control signal, and generates a first pre-emphasis output signal according to the first driving signal and the first pre-emphasis control signal. The second pre-emphasis unit receives a second driving signal and a second pre-emphasis control signal, and generates a second pre-emphasis signal according to the second driving signal and the second pre-emphasis control signal. The transmitter unit is coupled to a first output port a second port of the driving circuit, and is for receiving the first pre-emphasis signal and the second pre-emphasis signal.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Please refer to
The first bias component RA has a first node N11 coupled to a first reference voltage TXVDD and a second node N12 for outputting a first bias current IA. The second bias component RB has a first node N21 for draining a second bias current IB (which is identical to the first bias current IA in this exemplary embodiment) and a second node N33 coupled to a second reference voltage GND different from the first reference voltage TXVDD. The first pre-emphasis unit PE1 receives a first driving signal VD1 and a first pre-emphasis control signal VPC1, and generates a first pre-emphasis output signal VIP according to the first driving signal VD1 and the first pre-emphasis control signal VPC1. The first MOS transistor MN1 has a control node NA1 coupled to the first pre-emphasis unit PE1 for receiving the first pre-emphasis signal VIP generated from the first pre-emphasis unit PE1, a first connection node NB1 coupled to the second node N12 of the first bias component RA, and a second connection node NC1 coupled to a first output port of the driving unit 402. The second MOS transistor MN2 has a control node NA2 coupled to the second pre-emphasis unit PE2 for receiving the second pre-emphasis signal VIN generated from the second pre-emphasis unit PE2, a first connection node NB2 coupled to the second node N12 of the first bias component RA, and a second connection node NC2 coupled to a second output port of the driving unit 402. The third MOS transistor MN3 has a control node NA3 coupled to the second pre-emphasis unit PE2 for receiving the second pre-emphasis signal VIN generated from the second pre-emphasis unit PE2, a first connection node NB3 coupled to the first output port of the driving unit, and a second connection node NC3 coupled to the first node N21 of the second bias component RB. The fourth MOS transistor MN4 has a control node NA4 coupled to the first pre-emphasis unit PE1 for receiving the first pre-emphasis signal VIP generated from the first pre-emphasis unit PE1, a first connection node NB4 coupled to the second output port of the driving unit, and a second connection node NC4 coupled to the first node N21 of the second bias component RB.
As can be seen from the diagram, the first pre-emphasis unit PE1 receives the first driving signal VD1 and the first pre-emphasis control signal VPC1 to generate the first pre-emphasis signal VIP, and the second pre-emphasis unit PE2 receives the second driving signal VD2 and the second pre-emphasis control signal VPC2 to generate the second pre-emphasis signal VIN. The gates of the first and fourth MOS transistors (NMOS transistors) MN1 and MN4 are therefore connected to the first pre-emphasis signal VIP; and the gates of the second and third MOS transistors (NMOS transistors) MN2 and MN3 are therefore connected to the second pre-emphasis signal VIN. A clean and stable supply voltage TXVDD is provided via a buffer 401 with a bandgap reference voltage VREF. The first and second MOS transistors (NMOS transistors) MN1 and MN2 are connected to the supply voltage TXVDD via the first bias component (e.g., a resistor) RA in this embodiment; while the third and fourth MOS transistors (NMOS transistors) MN3 and MN4 are connected to a reference ground GND via the second bias component (e.g., a resistor) RB in this embodiment. When the first pre-emphasis signal VIP is high, the first current IA is conducted from the supply voltage TXVDD, flowing through the first bias component RA, the first MOS transistor MN1, the loads R1 and R2, the fourth MOS transistor MN4 and finally through the second bias component RB to the reference ground GND. Considering the impedance matching issue, to match the impedance of the load R1 at one side of the output node OP, an impedance towards the other side of the output node OP should be equal to the impedance of the load R1; namely, an on-resistance in series with the first bias component RA which is a resistor in this exemplary embodiment. Likewise, a proper matching at the output node ON can also be derived by adjusting the second bias component RB which is a resistor in this exemplary embodiment. Considering the MIPI standard, the supply voltage should be 0.4V whereas the loads R1 and R2 are both 50 ohms, and the resistance of the first and second bias components RA and RB are 50 ohms minus on-resistance of the first MOS transistor MN1 and 50 ohms minus on-resistance of the MOS transistor MN4, respectively. In an ideal case, the on-resistances of the MOS transistors are zero, and thereby the resistances of the first and second bias components (e.g., resistors) RA and RB are both 50 ohms. Therefore, in accordance with an exemplary embodiment of the present invention, a driving unit (i.e., a driver) consuming only 2 mA without sacrificing any operation performance is proposed. Compared with the conventional LDVS driver 300 in
Due to the process variation, on-chip resistors usually suffer from a 30% variation and cannot achieve a proper matching. Therefore, in order to calibrate the output impedances to be substantially 50 ohms, a conventional driver adopts a current mirror pair and an additional pin connecting to a more accurate external resistor for calibration. However, an additional pin and an external resistor imply an extra cost and are therefore not favorable for commercial consideration. Please refer to
Please refer to
The comparator 620 compares a voltage level of the output voltage VON and the target voltage VONR according to two clock signals P1 and P2, which are generated from the control logic 630, and thereby generates a comparison output ACT. In this embodiment, the comparator 620 includes a sampling and adjusting element 6201 and a determining element 6202. The sampling and adjusting element 6201 samples the target voltage VONR to generate a sampled voltage at an output node Nx according to the clock signal P1, and thereby adjusts the sampled voltage according to a difference between the target voltage VONR and the output signal VON to generate an adjusted voltage at the output node Nx. The determining element 6202 generates the comparison output ACT according to a voltage level at the output node Nx of the sampling and adjusting element 6201. The control logic 630 generates a control signal CTRL<N: 0> (please note that each of the control signal CTRL<N: 0> can also be utilized to control the power down state of corresponding pre-emphasis unit as the power down signal) to control the number of driving units to be activated according to the comparison output ACT.
An operation of the calibration unit 504 is detailed as follows. First of all, only one driving unit is activated, a calibration signal CAL is enabled and activates a clock generator 6301 within the control logic 630, and the clock generator 6301 generates two out-of-phase clock signals P1 and P2 according to a reference clock signal CLK. That is, the clock signal P2 is an inverse version of the clock signal P1. When the clock signal P1 is high (which implies that the clock signal P2 is low), the voltage level of the target voltage VONR is stored at Nx whereas a voltage level at Ny is fixed as low. When the clock signal P1 goes low (i.e., the clock signal P2 is high), the voltage level of the output voltage VON is introduced; if the output voltage VON is higher than the target voltage VONR, the voltage level at Nz is enhanced by an amount equal to a difference between VON and VONR, and the voltage level at Nx is thereby low and the voltage level at Ny is kept low; if the output voltage VON is lower than the target voltage VONR, the voltage level at Nz is lowered by an amount equal to a difference between VON and VONR, the voltage level at Nx is thereby high and the voltage level at Ny turns out to be high and triggers a following D flip-flop and activates the comparison output ACT to stop the clock generator 6301.
When the clock generator 6301 starts outputting clock signals P1 and P2, the clock signal P1 is transmitted to a counter 6302 within the control logic 630 to count accordingly until the comparison output ACT stops the clock generator 6301. A control signal generator 6303, which is a multiplexer in this embodiment, receives counting signals COUNT<N:0> from the counter 6302 and determines to output the counting signals COUNT<N:0> or manually-set signals MANUAL<N:0> as the control signal CTRL<N:0>. Please note that the embodiment above is only for illustrative purposes and is not supposed to be a limitation of the present invention. For example, the driving units 502 within the driving circuit 500 can utilize a thermometer-code method to distribute the output impedances of the driving units 502 in a binary fashion, and the control signal generator 6303 converts the counting signals COUNT<N:0> into a binary-type control signal to control the number of the driving units to be enabled.
The exemplary driving circuit 600 of the present invention activates only one driving unit in the beginning, which implies a relatively large voltage level at the output node ON, the clock generator 6301 starts generating clock signals P1 and P2, and the counter 6302 also starts counting up according to clock cycles of the clock signal P1 such that the control signal generator 6303 outputs the control signal to activate more driving units 502 within the driving circuit 500. The more driving units 502 are activated, the smaller the output impedance at the output node ON (since more output impedances of the driving units are connected in parallel), leading to a voltage drop of the output voltage VON at the output node ON. Once the output voltage VON is lower than the target voltage VONR, the comparator 620 enables a comparison output ACT to stop the clock generator 630, and the counter 6302 also stops counting. In this way, the number of the driving units needed to be enabled is determined.
Please refer to
Please refer to
The ratio generator 803 in this embodiment can be implemented using an XNOR logic gate with an enabling function. Please refer to
Please note that the first delay cell 801 and the second delay cell 802 provide a proper time delay for pre-emphasis functionality. For example, referring to
Please refer to
In accordance with exemplary embodiments of the present invention, a driving circuit, which has pre-emphasis and auto-calibration functionalities and is suitable for low-power high-speed operations, is provided. Adopting NMOS type transistors provides lower threshold voltage as well as lower power requirement, and the utilization of resistors as bias components provides proper matching with loads to be driven. Additionally, with the help of a simple on-chip calibration unit and a few pre-emphasis related components, no excessive cost is spent on additional pins and external resistors.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.
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|U.S. Classification||326/86, 326/26, 326/87, 326/82|
|International Classification||H03K19/094, H03K19/0175|
|Cooperative Classification||H03K19/018564, H03K19/018585|
|European Classification||H03K19/0185C2, H03K19/0185P|
|May 24, 2010||AS||Assignment|
Owner name: HIMAX IMAGING, INC., CAYMAN ISLANDS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:LIU, CHIH-MIN;YIN, PING-HUNG;HUANG, KUO-CHAN;REEL/FRAME:024426/0977
Effective date: 20091116
|Jun 18, 2014||FPAY||Fee payment|
Year of fee payment: 4